ENDOGENOUS SOURCE OF BACTERIA IN TRACHEAL TUBE AND PROXIMAL VENTILATOR BREATHING SYSTEM IN INTENSIVE-CARE PATIENTS

Although bacteria from both the ventilator breathing system and the ga strointestinal tract have been implicated in the pathogenesis of venti lator-associated pneumonia, an endogenous source of bacteria in the pr oximal respiratory breathing system has yet to be demonstrated conclus ively. We investigated a potential route of bacterial colonization fro m the stomach contents to the efferent limb of the ventilator breathin g system by bacterial culture of daily specimens from six sites in 20 surgical intensive care patients. Gram-negative bacilli were Isolated in a progressively increasing proportion of samples at successive samp ling points, consistent with an endogenous-to-external route of spread (patients, chi-square 14.12, P < 0.02; samples, chi-square 106.15, P < 0.001). Identical strains of gram-negative bacilli, confirmed by REP S typing, were found at two or more sites in seven patients. In all se ven, gram-negative bacilli were first isolated from a site In the pati ent. In none of the 20 patients was there evidence of a sequence of co lonization from the ventilator tubing or Y-piece connector towards the patient. Probable colonization sequences plotted from the time of fir st isolation supported the proposed sequence in six patients, and in f ive began with the stomach contents. Isolation sequences contrary to t he proposed direction of colonization involved four bacterial species and two patients, and did not extend beyond two sample sites. These fi ndings imply that the retrograde route of bacterial colonization of th e ventilated lung extends into the proximal respiratory breathing syst em and may help to identify additional targets for preventive interven tion.